Four-cylinder sheet-fed rotary offset press



y 1933- o. WOHLRABE 1,916,454

FOUR-CYLINDER SHEET FED ROTARY OFFSET PRESS Filed Sept 8, 1931 'UZ'Z'o W01 Zr aZe y I AZfZw-ney Patented July 4, 1933 UNITED" STATES OTTO 'WOHLRABE, F TLAUEN, (EEE'IEEBHLAILTY FOUR-CYLINDER SHEET-FED ROTARY OFFSET PRESS Application filed September 8, 1931, Serial No.

The present invention relates to a four cylinder rotary oifset press for sheets.

In four cylinder rotary ofiset machines, in which two adjacent rubber cylinders carry out simultaneously printing on front and perfecting as the rubber cylinder transferring the impression serve at the same time mutually as counterpression cylinders, care must be taken that the sheets do not come in contact with the impression before the printing takes place in order to prevent slurring of the fresh print. The difficulty is that one of the two rubber cylinders has to be provided with grippers capable of catching the sheet to be printed outside the printing point, and in order to prevent doubling of the color in view of this difficulty the invention provides that the rubber cylinder concerned be fitted with guide bars over which the sheet is drawn from the point where it is gripped by the cylinder grippers up to the printing point without coming in contact w1th the rubber cylinder concerned. Furthermore, the cylinder grippers are arranged radially adjustable in a manner known per 'se, so that they can catch the sheet outside the cylinder surface to draw its front edge up to the cylinder surface only in the immediate vicinity of the printing point.

One form of the invention is illustrated in the accompanying drawing, in which Figure 1 is a side view 0 the most essential parts of a sheet-fed four cylinder rotary ofl'set press; Fig. 2, a view of the cylinder grippers on a larger scale and at the moment when the front ed e of the sheet reaches the printing point; and Fig. 3, an axial section of the rubber cylinder and the gripper bar.

9 cylinders 1 and 2 and the rubber cylinders 3 and 4 serving mutually as counterpression cylinders, printing taking lace at the contact point of the two cylm ers.

- The sheets to be printed are fed to the rubber cylinder 4 in any suitable manner by hand or grippers or automatically by travellin bands and either kept in condition on the. fee ing table or separated in the known manner from a. reel inserted in the machine.

In the construction shown it is assumed The printing unit comprises the two plate 561,767, and in Germany September 16, 1980.

that the sheets on the table 5 are brought within reach of the oscillating preparatory grippers 6 b hand or feeding apparatus and then drawn rom the front edge of the table 5 within reach of the grippers 7 on the rubber cylinder 4. The grippers 7 are secured to the shaft 8 rotatably disposed in two carriages 9, each of which is displaceably arranged in a slot positioned approximately radially to the axis of the cylinder 4 inthe cylinder ends. Each of the two carriages 9 is provided with a roll 10 projecting laterally from the cylinder and engaging a groove 11 of the earns 12 or 13 secured to the machine frame and surrounding the shaft 15 of the cylinder 4., The grooves 11 in the two earns 12 and 13 are exactly alike and the two carriages 9 are thus always moved in the'same manner. To the projecting end of the shaft 8 a lever 16 is attached carrying a roll 17 engaging another groove 18 of the cam 12, whereby the gripper 7 is closed the moment the preparatory gripper 6 feeds the sheets thereto and opened again after printing at the very point where the sheets must be transferred to the delivery chain. The abutment against which the sheets are pressed by the grippers 7 to be passed through the printing zone is connected with the carriage 9. I To maintain the sheets secured by the grippers 7 out of contact with the rubber blanket mounted on the cylinder 4 for transferring the impression from the plate cylinder 2 to the sheets,- guide bars 20 are secured tothe cross beam 21 carried by the frame. Their free end is pointed and bent to hug the outer face of the cylinder 4. The number of guide bars 20 may be chosen at will.

The device described functions as follows: The sheets to be printed are fedby the preparatory grippers 6 to the cylinder grippers 7 and secured by the latter at the point shown in Fig. 1. For this purpose the two carriages 9 with the grippershaft 8,bymeans of the guide grooves 11 in the cams 12 and 13,

.are pushed beyond the circumference of the cylinder at to such an extent that the grippers 7 secure the sheets on the other side of the row of guide bars 20. During further rotation of the cylinder 4 the sheets are carried along by the grippers Tand drawn over the guide bars 20, and only'sh'ortly infront of the printing zone the carriages 9 with the gripper shaft 8, under the influence of the cams 12 and. 13, are drawn into thd rubber impression taken up by the rubber blanket rom the cylinder? can be effected in a per- "fe'ct manner without anyprevious' partial ber cylinderfl continues to rotate, ed sheet is finally passed over to the delii ery transfer of .the colors from the rubber blanket to'the sheet to be' printed. When the i ubthe printchain.

:The packing of the cylinder 4 may be chosen as required and consist of one or several rubberblankets, one edge of which is socured: to the tension shaft 31 while the other edge ieattached to a special shaft 32 or 33 so as. to permitindependent tensioning of the'blankets? To'render the shaft 31 accessible-in View of thegripper carriages 9 disposed in front thereof and their .gripper shaft 8, the guides of the carria es 9 are ar- 1n special ring members 34 rotatably supported on the bers. By releasing these adjusting or fixing members the two ring'members 34 can be. uniformly turned by the spindle 35 to move the carriages 9 with the shaft18 away from the tension shaft 31 for the blankets to render it accessible. Y

After the rubber blankets have been inountedas required,the gripper carriages 9 with the shaft 8 are brought back by the device described to thepoint where they are properly positioned during the operation of the machine. a I claim :f

1. Ina sheet-fed four cylinder rotary oil'- T .set press, two. offset cylinders, rubbenblanranged, not in slidesiof the cylin er, wall, but.

shaft 15 of the cylinder 4 and held in position by suitable adjusting memable manner on one of the said cylinders, means for operating the grippers to maintain the sheets to be printed, with the cooperation of the said the rubber b I ders' and to move inwardly to bring the sheets into contact with the said" blanket at the printing point.- only, ashaft carrying the sald. gl.ippers, and two carriages for the said I 4.- In a'sheet-fed four cylinder rotary ofl' setpress, two offset cylinders,'rubber blank8tS mounted on the said cylinders, guide bars associated with one of ders, arranged in an approximately radially adjustable manner on one of the said cylinders, and means for operating the'grippers to maintain the sheets to be printed, with the. cooperation of the said idezbars, out of contact with the rubber lanket of one of the said cylinders and to move inwardly to bring the sheets into contact with the said blanket at the printing point only;

5. ha sheet-fed'four cylinder rotary offset press, a pair of. ofi'set cylinders, a blanket mounted on each of the cylinders, guide bars associated With one of the cylinders, grip-- pers arranged in an approximately radially adjustable manner on one of the cylinders, and means for operating the grippers to maintain the sheets to be printed, with the cooperation of theguide bars, out of contact with the blanket of one of the cylinders andto move inwardly'to bring the sheets into contact with the said blanket only at the printing point.

In testimony whereof I have affixed my signature.

oTTo WOHLRABE.

uidebars, out of contact with anket of one of the said cylin- '5 the said cylin-. a shaft for the said cylinder, grippers 

